Unable to read data from table while generating ID number

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hi friends!!

i m trying to generate id using ASP.net + c# from sql server. I m getting these type of errors
"Invalid attempt to read when no data present"

while i have data in the table.

AFter some modification in code it is not able to insert the value i generate for ID in the table rather it is inserting 0 only.

 <pre lang="cs"> int id =0;
protected void Button1_Click(object sender, EventArgs e)
    {
        cm = new SqlCommand("select MAX(id) from login",cn);
        dr = cm.ExecuteReader();
        if(dr.Read()==false)
        id = Convert.ToInt32(dr[0].ToString());
        if (id == 0)
        {
            id = 1001;
            TextBox4.Text = id.ToString();
        }
        else {
            TextBox4.Text = dr[0].ToString();
            id = Convert.ToInt32(dr[0].ToString()) + 1;
        }
        dr.Close();
        TextBox3.Text = "My id is : "+id.ToString();
    }

i have assumption that user will have provide blank table where he will insert his live data then it should generate id number 1001, 1002, 1003 ... n ( i dont want to use auto increment)
code for insertion of data into table

<pre lang="cs">protected void Button3_Click(object sender, EventArgs e)
   {
       cm = new SqlCommand("insert into login values('" + TextBox2.Text + "','" + TextBox1.Text + "','" + id.ToString() + "')", cn);
       cm.ExecuteNonQuery();
   }

Plz give me your hints why it is generating such error

Posted 19-Jul-11 5:46am

NIKS SHINE

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3 solutions

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#realJSOP · Answer 1 · 2011-07-19T06:09:00

Solution 1

Invalid attempt to read when no data present

Try changing this:

if (dr.Read() == false)

to this

if (dr.Read())

Your current code is trying to do something if the reader does NOT read. that's backwards from what you actually want.

Posted 19-Jul-11 6:09am

#realJSOP

Updated 19-Jul-11 6:11am

v2

csharpbd · Answer 2 · 2011-07-19T07:44:00

Solution 2

try use this code:

C#

cm = new SqlCommand("select isnull(MAX(id),0) from login",cn);        
dr = cm.ExecuteReader();                  
if(dr.Read())                                                     
{
     id = Convert.ToInt32(dr[0].ToString());                                                
}

Posted 19-Jul-11 7:44am

csharpbd

Updated 19-Jul-11 7:46am

v2

NIKS SHINE · Answer 3 · 2011-07-19T08:08:00

Solution 3

it is still inserting 0 in the database... i could not understand why it is taking 0 in the dbo.table

Posted 19-Jul-11 8:08am

NIKS SHINE

Comments

Pete O'Hanlon 19-Jul-11 14:16pm

You are getting the maximum value, which means that you have to add one on to it. Suppose the maximum value is 3. If you get the max value, and then try to insert based on that, the max value is still 3.

NIKS SHINE 19-Jul-11 14:43pm

yes.. u r right, but may i know if there is any solution regarding this bug.. thanks

NIKS SHINE 19-Jul-11 14:30pm

yes, if 0 is the max value than again it is showing 0 in the table instead it should display or insert 1001...

NIKS SHINE 19-Jul-11 23:24pm

has resolved... partially